The present invention sets forth an improved process for encapsulating at least one piece of graphite within a glass or glass ceramic articles, in order, in particular, to improve heat spreading in glass ceramic cookware intended for direct heating on top of stoves, either gas or electric. With this improved process it is possible to make new products, not feasible with the encapsulation processes known until now, such as described, in particular, in the U.S. Pat. Nos. 4,248,925 and 4,260,405.
The above patents describe manufacturing of glass ceramic articles containing a graphite insert, said articles being cerammed around 900.degree. C. and intended for cooking on top of stoves.
At such ceramming temperatures, usually transparent glass ceramics are obtained, consisting of a stuffed .beta.-quartz solid solution. Nevertheless, it may be desirable to ceram at a higher temperature, around 1100.degree. C. to obtain an opaque glass ceramic, with a .beta.-spodumene structure, which is stronger and is a good substrate for decoration.